Hommes, femmes, intelligence :
un travail dérangeant
Les hommes sont en moyenne un peu plus intelligents que les femmes. Telle est la conclusion politiquement, psychologiquement et sexuellement très incorrecte que J. Philippe Rushton et al. tirent d'une étude sur 100.000 Américains ayant passé un test cognitif, le SAT (Scholastic Assessment Test). La différence est de 3,63 points de QI en faveur des jeunes mâles (sur une moyenne conventionnelle de 100 points, et avec un écart-type de 15 points environ, d'ailleurs un peu plus élevé chez les mêmes mâles que chez les femelles). En fait, plusieurs autres travaux récents avaient déjà trouvé cette différence.
Garçons et filles ont le même QI jusqu'à l'adolescence (12-15 ans), mais les garçons creusent peu à peu l'écart. La raison en est sans doute une maturation plus lente du cerveau, qui leur permet de gagner sur le tard quelques connexions neuronales dans la matière grise. Cette différence de QI se retrouve dans tous les niveaux socio-économiques et dans les sept groupes ethniques étudiés.
Rappel utile : ces mesure de moyennes sur des populations (échantillons larges) ne permettent évidemment pas de déduire des jugements individuels. Vous ne pouvez donc pas dire à votre copine ce soir : tu es moins intelligente que moi, cela signifierait que vous n'avez rien compris aux statistiques. Et que vous êtes probablement moins intelligent qu'elle. Mais ces résultats vont sans doute attiser les débats en cours aux Etats-Unis sur la rareté des femmes dans certaines postes scientifiques et techniques. Depuis un an que Lawrence Summers, président de Harvard, a suggéré que cette non-parité pourrait voir une base biologique, le psychodrame bat son plein outre-Atlantique.
Males have greater G: sex differences in general mental ability
A study of 100,000 17- to 18-year-olds on the SAT
At each and every every level of family income, for every level of fathers¹
and of mothers¹ education, and for each and every one of seven ethnic
groups, males had higher g scores than females
A study of 100,000 17- to 18-year-olds on the Scholastic Assessment Test
published in the September 2006 issue of the journal Intelligence, has
confirmed a surprising new finding-that men have a 4- to 5-point IQ
advantage over women by adulthood. Because girls mature faster than boys,
the sex difference is masked during the school years, which explains why the
sex difference was missed for 100 years.
A study published in the September 2006 issue of the journal Intelligence
analyzed 145 items from the Scholastic Assessment Test (SAT) in 100,000 17-
to 18-year-olds and found a male IQ advantage of 3.63 points.
It also found that the g factor--the general factor of mental ability
underlay both the SAT Verbal (SAT-V) and the SAT Mathematics (SAT-M) scales
with the congruence between these components greater than 0.90, and that it
was the g factor that predicted student grades better than the traditionally
used SAT-V and SAT-M scales.
The male and the female g factors were congruent in excess of .99, and they
favored males to an equivalent of 3.63 IQ points.
The male-female differences were present at every socioeconomic level, and
across several ethnic groups.
The average male advantage was found "throughout the entire distribution of
scores, in every level of family income, for every level of fathers' and of
mothers' education, and for each and every one of seven ethnic groups," said
J. Philippe Rushton, professor of psychology at the University of Western
Ontario, one of the authors of the study.
The paper's results dovetail with those from several other recently
published studies showing that men--surprisingly--have a 4- to 5- IQ point
advantage over women by late adolescence and early adulthood. Before that
age the two sexes are equal in general intelligence.
As such, the findings overturn a 100 year consensus that men and women
average the same in general mental ability.
Because girls mature faster than boys, the sex difference is masked during
the school years. Since almost all the data showing an absence of sex
differences were gathered on school children, this might explain why the sex
difference was missed for so long.
For decades, however, psychologists have accepted that men and women differ
in their test "profiles," with males averaging higher on tests of "spatial
ability" and females higher on tests of "verbal ability." These differences
were assumed to average out.
The authors of the study, psychologists Douglas N. Jackson and J. Philippe
Rushton at the University of Western Ontario, conducted the study because
two recent sets of observations had raised anew the question of sex
differences in general intelligence.
The first was that the general factor of mental ability--g--was found to
permeate all tests to a greater or lesser extent. Thus, a "spatial" test may
be relatively high on g (mental rotation) or low (perceptual speed), a
"verbal" test may be relatively high (reasoning) or low (fluency), as may a
"memory" test be high (repeating a series in reverse order) or low
(repeating a series in presented order).
More than any other factor, the test's g loading best determines a test's
power to predict academic achievement, creativity, career potential, and job
performance. Hence, the question of sex differences became formulated more
precisely as: "Are there sex differences on the g factor?"
Another set of observations concerned the sex difference found in brain size
and the relation between brain size and cognitive ability. Studies published
in 1992 at the University of Western Ontario by zoologist C. Davison Ankney,
and also by psychologist Rushton, showed men average a 100-gram advantage
over women in brain weight (and volume).
A 1997 study in Denmark documented that men have 15% more neurons than women
(22.8 versus 19.3 billion).
Over two-dozen Magnetic Resonance Imaging studies have confirmed a
brain-size/IQ correlation of about 0.40. So, if males average a larger
brain, shouldn't they also average a higher IQ score?
British psychologist Richard Lynn at the University of Ulster in Northern
Ireland, and Paul Irwing at the University of Manchester found that adult
men consistently average 4 to 5 IQ points higher than adult women in a
series of recent large-scale studies using a number of intelligence tests in
various countries. (Irwing & Lynn's most recent paper appeared in Nature on
July 6, 2006.)
Other researchers too have found a male advantage in general mental ability,
including Prof. Helmuth Nyborg at the University of Aarhus in Denmark, who
earlier this year was disciplined by his university for talking to the media
about his "politically incorrect" conclusions.
Prof. Rushton agreed that "these are unpopular conclusions." He said, "only
more data can determine the true nature of sex differences in cognitive
ability. However, people should not be made to feel afraid to study
Prof. Rushton accepted that sex differences in general mental ability could
help explain the "glass ceiling" phenomenon.
But he also noted the paradox that although men may have higher IQ scores,
women do increasingly well in school exams.
It will be very hard to argue that selection bias caused the sex difference
in this data set, the authors wrote. "That would require the assumption that
there are hypothetical respondents who, if tested, would provide a
compensating female-male advantage in g that would counterbalance the
findings. They would have to be found at every level of SAT performance, in
every level of family income, for every level of fathers' and of mothers'
education, and for every ethnic group examined."
Corresponding author: J. Philippe Rushton, Department of Psychology,
University of Western Ontario, London, Ontario, N6A 5C2, Canada Email:
Rushton@uwo.ca Tel: 519-661-3685
On the Web: Article pdf:
Full Citation: Jackson, D. N., & Rushton, J. P. (2006). Males have greater
g: Sex differences in general mental ability from 100,000 17- to
18-year-olds on the Scholastic Assessment Test. Intelligence, 34, 479-486.